does adderall(adderrall) cause long term heart problems?

I have been on adderall (adderrall) xr 30 mg once a day for about 3 or 4 years now. I just recently had to start taking the generic form and i have been experiencing rapid heart beat, shortness of breathe, and just feeling like i'm going to have a heart attack or something. I have had these symptoms before, and a few years ago i had an ekg, echocardiogram, stress test, breathing test, you name it.........i've had it, and everything was fine. My question is, should i be concerned about this? Is it because of the generic adderall (adderrall)? I have heard that generic medication can have anywhere between 80% to 120% of the drug in a pill......and that name brand's have to have exactly 100% of the drug. Could it be that with the generic i am getting a little more of the drug and that's why i am feeling this way? Does anyone know if adderall (adderrall) causes heart problems later down the road?